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Abstract

Cycling has been shown to confer considerable benefits in terms of health, leading
to reductions in death rates principally due to cardiovascular improvements and adaptation.

Given the disparity between the benefits of cycling on cardiovascular fitness and
previous research finding that cycling may not be beneficial for bone health, Hugo
Olmedillas and colleagues performed a systematic review of the literature. They concluded
that road cycling does not appear to confer any significant osteogenic benefit. They
postulate that the cause of this is that, particularly at a competitive level, riders
spend long periods of time in a weight-supported position on the bike.

Training programs may be supplemented with impact loading to preserve bone health;
however, the small increased risk of soft tissue injury must also be considered.

Keywords:

cycling; mountain biking; osteoporosis; anterior cruciate ligament

Introduction

Cycling has been shown to confer considerable benefits in terms of health. The replacement
of car trips with cycling and public transport use in Barcelona has led to a reduction
in overall deaths of 66.12 although there were an estimated increase in 1.15 deaths
due to air pollution and an additional 0.17 deaths due to road traffic fatalities
[1]. Notably the shift led to a reduction of CO2 203,251 t/CO2 emissions per year. Similar results were seen in the form of a reduction of 19.5 Disability
Adjusted Life Years in Copenhagen after the introduction of cycling to the place of
work or education [2]. These reductions in death rates are principally due to cardiovascular benefits.

In regard to health benefits, other body systems should be considered. Peak bone density
forms in the second and third decades and declines thereafter. Low bone mineral density
increases the risk of stress and fragility fractures as a result of the declining
bone density typically occuring in later life. Fragility fractures occur when the
ultimate tensile strength of bone is exceeded by the forces it is subjected to during
activities of daily living as well as the higher forces during falls. It is, therefore,
beneficial to optimize peak bone density during adolescence and early adult life during
bone formation. Bone will be optimally formed with impact loading according to Wolff's
law: that bone tissue forms and is remodelled in response to the mechanical forces
that it experiences [3].

When considering bone health, however, the impact of cycling is less beneficial than
other sports. Cycling may be considered to be a non-impact sport with reduced weight
bearing, and as a result may be expected to lead to comparatively reduced bone density.
Given the disparity between the benefits of cycling on cardiovascular fitness and
some previous research findings that cycling may not be beneficial for bone health,
Hugo Olmedillas and colleagues performed a systematic review of the literature [4].

Sports and bone health: what are the effects?

This systematic review included 31 studies that analyzed bone mass and bone metabolism
in cyclists across four databases. The authors concluded that road cycling does not
appear to confer any significant osteogenic benefit. They postulate that the cause
of this is that, particularly at a competitive level, riders spend long periods of
time in a weight-supported position on the bike. It is hypothesized that this, in
combination with a necessary enforced recovery time involving a large amount of time
sitting or lying supine, results in low bone mineral density due to a lack of impact
[4].

How do the findings of this study influence bone health in cyclists? The clinical
implications may not be as clear as one would imagine. For instance, the vast majority
of cyclists do not compete at a competitive level and off-road cycling may be more
popular in the age group during which peak bone mass is optimized. The choice of bike
may also influence bone health. Suspension systems are currently fashionable with
bikes being classified as rigid, hard tail or front suspension. With increased suspension,
muscular stress has been noted to be increased [5], although no studies have been undertaken regarding bone stress.

Weight bearing exercise is known to be beneficial for long-term bone health and adolescents
and adults participating in endurance sports have been shown to have a lower bone
mineral density than those participating in ball and power sports [6]. High loading sports such as gymnastics, hurdling, judo, karate and other jumping
sports lead to higher bone mineral composition, bone mineral density and enhanced
bone geometry specifically related to the sports participated in. Football, basketball,
racquet games and step aerobics are described as having odd impact loading and swimming
and cycling as non-impact sports [7]. Similarly, collegiate gymnasts have been shown to have significantly higher bone
mineral density (BMD) compared to cross country runners [8].

Although beneficial for bone health, high and odd impact sports have been associated
with increased risk of anterior cruciate ligament injury. Team handball played by
both sexes has one of the highest injury rates, with as many as 2.29 anterior cruciate
ligament (ACL) injuries per 1,000 match hours in Norwegian female elite competition
[9]. Injury rates in the at-risk population aged 16 to 39 years are as much as 85 per
100,000 and occur in females with a frequency of four times that of males [10]. While reconstructive surgery may allow participants to return to sports activity,
this does not occur in every case [11]. Thus, young females may be encouraged to return to non-pivoting, low impact sports,
such as swimming and cycling. It is also worthy of note that following ACL injury,
the bone mineral density declines in the injured leg and does not return to that of
the non-injured leg even after muscular strength returns to normal [12,13].

Conclusions

Competitive endurance cycling may be considered to have benefits for health but meta-analyses
confirm that this does not extend to bone health. Training programs may be supplemented
with impact loading to preserve bone health; however, the increased risk of ligamentous
injury must be considered with the participation in pivoting sports.

Abbreviations

ACL: anterior cruciate ligament; BMD: bone mineral density.

Competing interests

The author declares that they have no competing interests.

Authors' information

MC is a Consultant Trauma and Orthopaedic Surgeon with a specialist interest in Sports
Injuries and Sports Medicine. He is also President of the British Orthopaedic Sports
Trauma and Arthroscopy Association.